[lld][MachO] Fix a suspicous assert in SyntheticSections.cpp

This was comparing some .size() (uint64_t) against the sizeof a size_t
which changes with system bitness. This produced a warning that
brought this to my attention.

These tests were failing too on 32 bit Arm only:
  lld :: MachO/objc-category-merging-complete-test.s
  lld :: MachO/objc-category-merging-minimal.s

The assert I think meant to check the value of target->wordSize,
not the size of its type. Which is a type that changes size between
systems.

Author: DavidSpickett

lld/MachO/SyntheticSections.cpp

@@ -2119,7 +2119,7 @@ void ObjCMethListSection::writeRelativeOffsetForIsec(
     assert(selRef && "Expected all selector names to already be already be "
                      "present in __objc_selrefs");
     symVA = selRef->getVA();
-    assert(selRef->data.size() == sizeof(target->wordSize) &&
+    assert(selRef->data.size() == target->wordSize &&
            "Expected one selref per ConcatInputSection");
   } else if (reloc->referent.is<Symbol *>()) {
     auto *def = dyn_cast_or_null<Defined>(reloc->referent.get<Symbol *>());